Precise station positions from VLBI observations to satellites: a simulation study   总被引：1，自引：1，他引：0  

Lucia Plank  Johannes Böhm  Harald Schuh 《Journal of Geodesy》2014,88(7):659-673

Very long baseline interferometry (VLBI) tracking of satellites is a topic of increasing interest for the establishment of space ties. This shall strengthen the connection of the various space geodetic techniques that contribute to the International Terrestrial Reference Frame. The concept of observing near-Earth satellites demands research on possible observing strategies. In this paper, we introduce this concept and discuss its possible benefits for improving future realizations of the International Terrestrial Reference System. Using simulated observations, we develop possible observing strategies that allow the determination of radio telescope positions in the satellite system on Earth with accuracies of a few millimeters up to 1–2 cm for weekly station coordinates. This is shown for satellites with orbital heights between 2,000 and 6,000 km, observed by dense regional as well as by global VLBI-networks. The number of observations, as mainly determined by the satellite orbit and the observation interval, is identified as the most critical parameter that affects the expected accuracies. For observations of global positioning system satellites, we propose the combination with classical VLBI to radio sources or a multi-satellite strategy. Both approaches allow station position repeatabilities of a few millimeters for weekly solutions.  相似文献   

Seismic behavior of three-leaf stone masonry buildings before and after interventions: Shaking table tests on a two-storey masonry model   总被引：1，自引：1，他引：0  

Elizabeth Vintzileou  Charalambos Mouzakis  Chrissy-Elpida Adami  Lucia Karapitta 《Bulletin of Earthquake Engineering》2015,13(10):3107-3133

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An experimental study on the apparent viscosity of sandy soils: from liquefaction triggering to pseudo-plastic behaviour of liquefied sands     

Mele  Lucia 《Acta Geotechnica》2022,17(2):463-481

Acta Geotechnica - The complete loss of soil strength and stiffness, which occurs during soil liquefaction, marks a change of state of the soil that switches from solid to liquid. In particular,...  相似文献   

Identification of accelerometric stations in ITACA with distinctive features in their seismic response     

Dino Bindi  Lucia Luzi  Francesca Pacor  Roberto Paolucci 《Bulletin of Earthquake Engineering》2011,9(6):1921-1939

In this work, we analyze the records of the Italian strong motion database (ITACA, ) with the aim of identifying stations affected by site effects that are not captured by standard seismic classification schemes. In particular, we consider four different site classifications, two of them based on geological/geophysical characteristics and two driven by data. For each classification we develop a ground motion prediction equation using a random effect approach to isolate the between-station and within-station distribution of errors. The site coefficients obtained for the different classes confirm that site amplification effects are significant for both the horizontal and vertical components. The between-station error normalized to the standard deviation of the between-station error distribution is then used to identify stations characterized by large errors, attributable to site effects not accounted for by the classification schemes. The results show that large errors can affect the predictions when the site effects are not uniquely related to the reduction of the seismic impedance in the uppermost layers. For example, amplifications of ground motion over the long period range are observed for stations installed within alluvial closed-shape basins, as consequence of locally generated surface waves. For these stations, classifications based on the horizontal to vertical response spectra ratio are not reliable, since amplifications are also affecting the vertical component. Another interesting feature which emerges from the analysis is the significant de-amplification of short period spectral ordinates that seems to be related to stations typically set in at the foundation level of massive structures. To increase the usefulness of the data set, the most important distinctive features of the strong motion stations are documented in the ITACA database reports containing the instrument information and the available geological-geotechnical data.  相似文献   

Reconstruction of the eruptive activity on the NE sector of Stromboli volcano: timing of flank eruptions since 15 ka   总被引：1，自引：0，他引：1  

Sonia Calvari  Stefano Branca  Rosa Anna Corsaro  Emanuela De Beni  Lucia Miraglia  Gianluca Norini  Jan Wijbrans  Enzo Boschi 《Bulletin of Volcanology》2011,73(1):101-112

A multidisciplinary geological and compositional investigation allowed us to reconstruct the occurrence of flank eruptions on the lower NE flank of Stromboli volcano since 15 ka. The oldest flank eruption recognised is Roisa, which occurred at ~15 ka during the Vancori period, and has transitional compositional characteristics between the Vancori and Neostromboli phases. Roisa was followed by the San Vincenzo eruption that took place at ~12 ka during the early stage of Neostromboli period. The eruptive fissure of San Vincenzo gave rise to a large scoria cone located below the village of Stromboli, and generated a lava flow, most of which lies below sea level. Most of the flank eruptions outside the barren Sciara del Fuoco occurred in a short time, between ~9 and 7 ka during the Neostromboli period, when six eruptive events produced scoria cones, spatter ramparts and lava flows. The Neostromboli products belong to a potassic series (KS), and cluster in two differently evolved groups. After an eruptive pause of ~5,000 years, the most recent flank eruption involving the NE sector of the island occurred during the Recent Stromboli period with the formation of the large, highly K calc-alkaline lava flow field, named San Bartolo. The trend of eruptive fissures since 15 ka ranges from N30°E to N55°E, and corresponds to the magma intrusions radiating from the main feeding system of the volcano.  相似文献   

Reactivity of sandstone and siltstone samples from the Ketzin pilot CO2 storage site-Laboratory experiments and reactive geochemical modeling     

Sebastian Fischer  Axel Liebscher  Marco De Lucia  Lutz Hecht 《Environmental Earth Sciences》2013,70(8):3687-3708

To evaluate mineralogical-geochemical changes within the reservoir of the Ketzin pilot CO₂ storage site in Brandenburg, Germany, two sets of laboratory experiments on sandstone and siltstone samples from the Stuttgart Formation have been performed. Samples were exposed to synthetic brine and pure CO₂ at experimental conditions and run durations of 5.5 MPa/40 °C/40 months for sandstone and 7.5 MPa/40 °C/6 months for siltstone samples, respectively. Mineralogical changes in both sets of experiments are generally minor making it difficult to differentiate natural variability of the whole rock samples from CO₂-induced alterations. Results of sandstone experiments suggest dissolution of the anorthite component of plagioclase, anhydrite, K-feldspar, analcime, hematite and chlorite + biotite. Dissolution of the anorthite component of plagioclase, anhydrite and K-feldspars is also observed in siltstone experiments. In an inverse modeling approach, an extensive set of equilibrium simulations was set up in order to reproduce the experimental observations of the sandstone experiments. Simulations generally show fairly good matches with the experimental observations. Best matches with measured brine data are obtained from mineral combinations of albite, analcime, anhydrite, dolomite, hematite, illite, and kaolinite. The major discrepancies during equilibrium modeling, however, are reactions involving Fe²⁺ and Al³⁺. The best matching subsets of the equilibrium models were finally run including kinetic rate laws. These simulations reveal that experimentally determined brine data was well matched, but reactions involving K⁺ and Fe²⁺ are not fully covered. The modeling results identified key primary minerals as well as key chemical processes, but also showed that the models are not capable of covering all possible contingencies.  相似文献   

Modelling galaxy clustering in a high-resolution simulation of structure formation     

Lan Wang  Cheng Li  Guinevere Kauffmann  Gabriella De Lucia 《Monthly notices of the Royal Astronomical Society》2006,371(2):537-547

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The many lives of active galactic nuclei: cooling flows, black holes and the luminosities and colours of galaxies   总被引：2，自引：0，他引：2  

Darren J. Croton  Volker Springel  Simon D. M. White  G. De Lucia  C. S. Frenk  L. Gao  A. Jenkins  G. Kauffmann  J. F. Navarro  N. Yoshida 《Monthly notices of the Royal Astronomical Society》2006,365(1):11-28

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Iron release in aqueous environment by fresh volcanic ash from Mount Etna (Italy) and Popocatépetl (Mexico) volcanoes     

Giancarlo Capitani  Nobuyoshi Miyajima  Roberto Sulpizio  Maria D’Addabbo  Lucia Galimberti  Massimo Guidi  Giovanni B. Andreozzi 《Environmental Earth Sciences》2018,77(13):521

In this study, we performed leaching experiments for timescales of hours-to-months in deionized water on fresh volcanic ash from Mt. Etna (Italy) and Popocatépetl (Mexico) volcanos to monitor Fe release as a function of ash mineral chemistry and size, with the aim of clarifying Fe release mechanisms and eventually evaluating the impact of volcanic ash on marine and lacustrine environments. To define sample mineralogy and Fe speciation, inclusive characterization was obtained by means of XRF, SEM, XRPD, EELS and Mössbauer spectroscopies. For Etna and Popocatépetl samples, glass proportions were quantified at 73 and 40%, Fe₂O₃ total contents at 11.6–13.2 and 5.8 wt%, and Fe³⁺/Fe_Tot ratios at 0.33 and 0.23, respectively. Leaching experiments showed that significant amounts of iron, ~?30 to 150 and ~?750 nmol g^?1 l^?1 for pristine Etna and Popocatépetl samples, respectively, are released within the first 30 min as a function of decreasing particle size (from 1 to 0.125 mm). The Popocatépetl sample showed a very sustained Fe release (up to 10 times Etna samples) all along the first week, with lowest values never below 400 nmol g^?1 l^?1 and a maximum of 1672 nmol g^?1 l^?1 recorded after 5 days. This sample, being composed of very small particles (average particle size 0.125 mm) with large surface area, likely accumulated large quantities of Fe-bearing sublimates that quickly dissolved during leaching tests, determining high Fe release and local pH decrease (that contributed to release more Fe from the glass) at short timescale (hours-to-days). The fractional Fe solubility (Fe_S) was 0.004–0.011 and 0.23% for Etna and Popocatépetl samples, respectively, but no correlation was found between Fe released in solution and either ash Fe content, glass/mineral ratio or mineral assemblage. Results obtained suggest that volcanic ash chemistry, mineralogy and particle size assume a relevant role on Fe release mostly in the medium-to-long timescale, while Fe release in the short timescale is dominated by dissolution of surface sublimates (formed by physicochemical processes occurring within the eruption plume and volcanic cloud) and the effects of such a dissolution on the local pH conditions. For all samples, a moderate to sustained Fe release occurred for leaching times comparable with their residence time within the euphotic zone of marine and lacustrine environments (variable from few minutes to few hours), revealing their possible contribution to increase Fe bioavailability.  相似文献   

Sedimentation rate of soil microparticles     

Milan Gomboš  Andrej Tall  Jarmila Trpčevská  Branislav Kandra  Dana Pavelkova  Lucia Balejčíková 《Arabian Journal of Geosciences》2018,11(20):635

The aim of the submitted paper is to identify the lower limit of Stokes’ law for calculating the deposition rate of soil microparticles. The authors’ hypothesis on the lower limit of Stokes’ law is based on the idea that with the gradual formation of the colloidal dispersion system, both the particle size and the sedimentation rate decrease. It is assumed that under the lower particle size limit, Stokes’ law does not apply. As a result of the diffusion, the state of the sedimentation equilibrium gradually emerges. The results of the experiment showed that in laboratory conditions, Stokes’ equation ceases to be valid for sedimentation of the particles sized d(90)?<?2 μm. During the experiment, a dynamic sedimentation equilibrium was reached at the particle size d(90)?=?0.27 μm. The scientific contribution of this knowledge is the accuracy of the determination of hydropedological characteristics dependent on the texture of the soil. In this context, the results stated in the paper define the lower limit of the validity for the laboratory procedures determining soil texture on the basis of the sedimentation methods. To identify the textures below this limit, it is necessary to choose the methods based on other principles. Determination of the lower limit is particularly important in clay soils containing a high proportion of clay particles (clay particles <?2 μm).  相似文献